Spells are unpredictable, no one knows how long a spell will take. Sense magic(k) is energy..it will take as long as it must.
No, It could depends, It's impossible to tell when a spell will occure, but you will know when it does.
No, as I said it's unpredictable. Even the word "immediatly" will not change the paste of magic(k). Again words don't really matter in spell casting, it's visualization on what you want, belief in magic(k), and believing in your spell.
Even if so, the spell will take as much time as it needs.